1. Field of the Invention
This invention relates to flexible printed circuit boards having electrically conducting patterns formed on both sides thereof.
2. Description of the Prior Art
Two-sided flexible printed circuit boards, because the patterns of electrical conduction on the front and back surfaces have heretofore very often happened to coincide in place with each other across the substrate, and further because electrical elements such as IC units, resistors and condensers have been installed on each side, are more rigid than one-sided flexible printed boards.
To install the two-sided flexible printed board in a curved form, therefore, a difficult problem has arisen that the radius of curvature of the curved portion cannot be made as small as is needed. Due to the stress at, or near the curved portion being very great, no IC units, resistors or condensers can be positioned in this weakened curved portion without causing a large decrease in integrity. Also, through-holes cannot be bored therein.
If the radius of curvature of the curved portion is decreased by transferring the patterns on the back surface to the front surface, or vice versa, through-holes must be provided. Thus, another drawback is produced that the availability of a space for additional necessary lines of electrical conduction is lost.